What child doesn't love a game of hide-and-seek? How about a high-tech version in which members of a global treasure-hunting community hide small treasures the child can seek out using a smartphone?

That's what geocaching is all about: It's a free, real-world game in which players use a GPS-enabled mobile device to navigate to a specific location — maybe even the local park — to find a hidden container, or "geocache," that another player placed. The geocache contains a logbook to sign and very often a real treasure, perhaps a small trinket or toy. You can take the item with you as long as you replace it with another item of the same or greater value.

Websites provided: http;//www.geocaching.com, to locate, research, and log finds. And help guides to get started: http://www.geocaching.com/guide